502 The Philippine Journal of Science 1914 
There was no positive evidence of the dynamic activities of 
Diplachne until after the persistent high hot water following 
the heavy rains of September, 1914. The high water killed con- 
siderable vegetation in the vicinity of the hot water vents. Re- 
invasion of plants began soon after the water cooled. Bacteria 
and blue-green algae in the water and Bacopa above the water 
were the pioneers. The latter was generally followed by Fim- 
bristylis spathacea, but in a very few places Diplachne invaded 
the Bacopa. 
On the banks of streams this association readily gives way to 
others, but as a rule it does not show indications of succession. 
A radical lowering of the water table to below the surface of the 
ground would lead to its elimination, but the mere drying up of 
the streams during the dry season — a condition which is also 
unfavorable for rapid advances of other vegetation — does not 
materially affect it. A permanent lowering of the water makes 
the habitat favorable for the reinvasion of the Bacopa-Lippia 
association, represented especially by Lippia. 
As a pioneer invader in two of the hot springs in the Tarlac 
area this association was sparingly represented by plants of 
Diplachne fusca Beauv., rooted below the surface in lukewarm 
water. This species is adapted to fluctuations in water level, 
but very high water would entirely submerge it, and hot water 
would kill it. Wherever it occurs the structure of the association 
is very simple. 
THE IPOMOEA REPTANS ASSOCIATION 
This semiaquatic association in which the plants are generally 
rooted in damp ground just above the water level, but with long 
stems which run out over the water, was represented in the 
Tarlac area in 1913 at one of the hot springs near the railroad. 
Ipomoea reptans Poir. rooting back of Diplachne, sends out 
runners under it into the hot water. There the tips are killed 
back. In this locality there were no secondary species, but 
where this association occurs along ponds or along Lake Bay, 
the stems catch floating aquatics and debris of all sorts. 
In the high hot water of September, 1914, all of this association 
in the Tarlac area was killed. The association is not present in 
the vicinity of the Los Bafios springs. 
THE FIMBRISTYLIS MILIACEA ASSOCIATION 
Occupying a limited area at water-table level in the eastern 
part of the Los Banos area is a small patch of an association 
